In the manufacture of electronic devices such as integrated circuits, a target substrate, such as a semiconductor wafer, is subjected to various processes, such as film formation, etching, oxidation, diffusion, reformation, annealing, and natural oxide film removal. Silicon-containing films are an important part of many of these processes.
Silicon-containing films are used for a wide variety of applications in the semiconductor industry. Examples of silicon-containing films include epitaxial silicon, polycrystalline silicon (poly-Si), and amorphous silicon, epitaxial silicon germanium (SiGe), silicon germanium carbide (SiGeC), silicon oxide (SiO), silicon carbide (SiC), silicon nitride (SiN), silicon oxynitride (SiON), silicon carbonitride (SiCN), and silicon carboxide (SiCO). As circuit geometries shrink to smaller feature sizes, thinner films with better coverage on high aspect ratio structures are required. As device technology advances, metallization schemes also are more sophisticated and require lower thermal stresses. Therefore, lower deposition temperatures for Si-containing films are preferred.
Silicon nitride films have very good oxidation resistance and dielectric qualities. Accordingly, these films have been used in many applications, including oxide/nitride/oxide stacks, etch stops, oxygen diffusion barriers, and gate insulation layers, among others. Conformal coverage with low pattern loading effect of dielectric films on high aspect ratio structures are of critical requirement as device node shrinks down to below 45 nm.
Several methods are known for forming a silicon nitride film on the surface of a semiconductor wafer by chemical vapor deposition (CVD). In thermal CVD, a silane gas, such as monosilane (SiH4) or polysilanes, is used as a silicon source gas. However, CVD processes often result in non-conformal films.
Silicon nitride films from furnace processes offer good conformality. However, the drawbacks include high temperature requirement (≥550° C.), lack of wafer-to-wafer uniformity and few capabilities to engineer film compositions and properties especially stress for different applications.
Silane-based plasma enhanced chemical vapor deposition (PE-CVD) high tensile stress nitride films have been proven to improve carrier mobility, and thus device performance. However, the films have poor step coverage due to directionality of radical fluxes. As a result, the improvement effect is diminished when device dimension reduces.
Atomic layer deposition (ALD) processes offer much improved conformality and pattern loading than CVD processes. SiN film formation has also been carried out via ALD with halogenated silane precursors and ammonia in furnace type reactors. However, this process requires high temperatures, in excess of 550° C., to effect clean conversion and eliminate NH4X byproducts. In device manufacturing, processes that can be performed at lower temperatures are generally desired for thermal budget and other reasons.
Accordingly, there is a need for a low-temperature deposition process which can offer highly conformal SiN-containing films, while also addressing any of the other currently problems described above.